The content of Application No. TOKUGANHEI 9-178495 filed Jul. 3, 1997, in Japan is hereby incorporated by reference.
The present invention relates to a noise reducing device for an internal combustion engine of an automobile, etc., and particularly relates to an intake noise reducing device capable of improving comfortableness by reducing noises of an intake system.
In a related intake system, an air introducing duct is divided into two sections and a valve is attached to one duct of the sections. The valve is opened and closed in accordance with a change of engine speed, etc. (See Japanese Laid-Open Patent Nos. 3-290052 and 4-8861.)
In one of the above related intake systems, a resonance silencer is formed by closing the valve in low speed rotation so that silencing effects with respect to a specific frequency are obtained (see Japanese Laid-Open Patent No. 3-290052). In the other, duct resonance from 200 to 300 Hz is reduced by a side branch (Japanese Laid-Open Patent No. 4-8861). Therefore, it is difficult to sufficiently reduce noises in a wide frequency range from a lower frequency.
The present invention is achieved with such points in view. It therefore is an object of the present invention is to provide an intake noise reducing device for an internal combustion engine capable of silencing noises in a wide range from a low frequency to an intermediate frequency, which is normally hearable by a human being.
An intake noise reducing device for an internal combustion engine in the present invention has a duct, a partition wall, a silencer, a connecting duct and a valve. The duct introduces air into an internal combustion engine and has a length L. The partition wall is arranged within the duct to divide into first and second sections and has a length equal to or greater than L/2. The connecting duct connects the first section and the silencer. A connecting position of the connecting duct to the duct is in opposite to the partition wall. The valve opens and closes the second section.
In the above construction, for low engine loads, the valve of the second section is closed. As a result, the silencing effects are increased in a frequency area from low to high. Accordingly, silencing performance is greatly improved over a wide range of frequency and the intake noises are greatly reduced and quietness is improved in an ordinary low load driving condition in which operating frequency is high.
For high engine loads, the valve of the second section is opened. As a result, a required engine output is secured and excellent silencing performance is exhibited in comparison with a conventional structure having no partition wall.
Accordingly, silencing performance is greatly improved over a wide range of frequency and intake noises are greatly reduced.